In addition to the drive unit, secondary appliances, which likewise have to be supplied with electrical power, may be arranged in a locomotive or else in the cars connected to the locomotive. One such secondary appliance, by way of example, may be a fan. Since these secondary appliances require a lower electrical voltage than the drive unit, it has until now been normal to use an auxiliary generator which is designed for the voltage required by the secondary appliances, and is connected to the diesel engine in precisely the same way as the generator which is intended for the drive unit.
The use of two generators in a diesel-electric locomotive is complex. This is due to the fact that a generator contains rotating parts, as a result of which it not only has a high procurement price, but must also be maintained and repaired, which is costly.
Despite these disadvantages, two generators have always been installed in a diesel-electric locomotive, for a very long time period.